EP0248993B1 - Mémoire dynamique structurée verticalement à haute densité - Google Patents

Mémoire dynamique structurée verticalement à haute densité Download PDF

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Publication number
EP0248993B1
EP0248993B1 EP87104940A EP87104940A EP0248993B1 EP 0248993 B1 EP0248993 B1 EP 0248993B1 EP 87104940 A EP87104940 A EP 87104940A EP 87104940 A EP87104940 A EP 87104940A EP 0248993 B1 EP0248993 B1 EP 0248993B1
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EP
European Patent Office
Prior art keywords
bit
trench
disposed
set forth
sidewall
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP87104940A
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German (de)
English (en)
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EP0248993A1 (fr
Inventor
Brian F. Fitzgerald
Kimm Yen T. Nguyen
Van S. Nguyen
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International Business Machines Corp
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International Business Machines Corp
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Publication of EP0248993A1 publication Critical patent/EP0248993A1/fr
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
    • G11C11/21—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements
    • G11C11/34—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices
    • G11C11/40—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors
    • G11C11/401—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors forming cells needing refreshing or charge regeneration, i.e. dynamic cells
    • G11C11/403—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors forming cells needing refreshing or charge regeneration, i.e. dynamic cells with charge regeneration common to a multiplicity of memory cells, i.e. external refresh
    • G11C11/404—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors forming cells needing refreshing or charge regeneration, i.e. dynamic cells with charge regeneration common to a multiplicity of memory cells, i.e. external refresh with one charge-transfer gate, e.g. MOS transistor, per cell
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10B—ELECTRONIC MEMORY DEVICES
    • H10B12/00—Dynamic random access memory [DRAM] devices
    • H10B12/30—DRAM devices comprising one-transistor - one-capacitor [1T-1C] memory cells
    • H10B12/37—DRAM devices comprising one-transistor - one-capacitor [1T-1C] memory cells the capacitor being at least partially in a trench in the substrate

Definitions

  • This invention relates to vertically structured dynamic memories according to the preamble of claim 1, and as e.g. known from US-A-4225945.
  • Integrated semiconductor memory circuits particularly those employing cells which include essentially a storage capacitor and a switch have achieved high memory cell densities.
  • One of the simplest circuits for providing a small dynamic memory cell is described in commonly assigned U.S. Patent No. 3,387,286, filed July 14, 1967, by R.H. Dennard.
  • Each cell employs a storage capacitor and a field effect transistor acting as a switch to selectively connect the capacitor to a bit/sense line.
  • U.S. Patent 4,222,062 filed on May 4, 1976, discloses a memory cell structure wherein a switching device is formed near the bottom of a trench with the bit line and storage capacitor located at a wall of the trench.
  • a dynamic random access memory wherein each cell has a storage capacitor and switching device and a bit/sense line or plate located along a sidewall of a trench formed in a semiconductor substrate.
  • the trench width defines the length of the switching device, with the storage capacitor and a highly conductive bit/sense line being formed along opposite sidewalls of the trench.
  • the highly conductive bit/sense line or plate interconnecting a large number of the cells of the array extends continuously from cell to cell within the trench at a sidewall thereof.
  • the storage capacitors of these many cells have a highly conductive common plate extending continuously within the trench at the opposite sidewall.
  • Fig. 1 a circuit diagram of a well known one device dynamic memory cell 10 which includes a field effect transistor 12 having a gate 14, a storage capacitor 16 having a conductive plate 18 and a storage node 20, and a bit/sense line 22.
  • a high or low voltage is applied to the bit/sense line 22 and the transistor 12 is turned on to charge the storage node 20 if a high voltage was applied to the bit/sense line 22, indicating the prsence of, say, a 1 digit, otherwise the storage node 20 remains uncharged, indicating the presence of a stored 0 digit.
  • bit/sense line 22 To read information from the storage capacitor 16, the bit/sense line 22 is charged to an intermediate voltage and the transistor 12 is turned on. If the bit/sense line 22 is discharged, a sense amplifier (not shown) connected to the bit/sense line 22 will indicate the presence of a 0 digit in the storage capacitor 16, otherwise the storage capacitor 16 was storing a 1 digit.
  • a novel vertical structure of the memory circuit of Fig. 1 is illustrated in Figs. 2 and 3, wherein Fig. 3 is a plan view of the structure and Fig. 2 is a sectional view taken through line 2-2 of Fig. 3.
  • the field effect transistor 12, the storage capacitor 16 and the bit/sense line 22 are all located within a trench 24 formed in a semiconductor substrate 26, preferably made of silicon and having a P- conductivity.
  • the transistor 12 includes the gate 14 which is preferably doped polysilicon or titanium silicide (TiSi2) separated from the bottom of the trench 24 by thin insulating layer 28 preferably made of silicon dioxide or silicon oxynitride.
  • the storage capacitor 16 includes the storage node 20 made in the form of an N+ diffusion region disposed generally along a sidewall of the trench 24 and the conductive plate 18, which may be a metallic layer of, e.g., copper-doped aluminum or titanium silicide, separated from the N+ diffusion region 20 by an insulating layer 30 preferably also made of silicon dioxide.
  • An N+ diffusion region 32 similar to that of the N+ diffusion region 20 is formed on the sidewall of the trench 24 opposite to the sidewall in which region 20 is formed.
  • the N+ diffusion region 32 serves as the drain of the transistor 12.
  • the bit/sense line 22 is disposed along the same sidewall as the drain diffusion region 32 and in electrical contact with region 32.
  • the bit/sense line 22 is a highly conductive plate or film, preferably made of copper-doped aluminum or titanium silicide.
  • a layer of insulation 36 is formed over the capacitor plate 18, the bit/sense line plate 22 and over the surface of the silicon substrate 26 so as to insulate the gate 14 of transistor 12 from the conductive plates 18 and 22.
  • a word line 38 to which the gate 14 may be integrally connected is disposed over the insulating layer 28.
  • the word line 38 is also preferably made of doped polysilicon or titanium silicide. As can be seen in Fig.
  • first segments of insulation 40 are disposed adjacent to the silicon substrate 26 within an isolation trench 42 extending along the edges of the word line 38 and second segments of insulation 44 are disposed adjacent to the gate 14 within the isolation trench 42 along the edges of the word line 38.
  • the first segments of insulation 40 are preferably made of silicon dioxide and the second segments of insulation 44 are preferably made of cured polyimide.
  • a very compact one device dynamic memory cell has been made in a vertical structure wherein all elements of the cell are located within a trench.
  • the trench may be made as deep and as wide as necessary to provide a storage capacitor of desired size, to provide a bit/sense line of desired conductivity and to provide a transistor of desired switching characteristics.
  • the depth of the trench 24 is preferably 1.3 microns with a width of also 1.3 microns, and the width of the channel of the transistor 12 likewise being 1.3 microns, with the length of the channel being equal to 1.3 microns minus the thicknesses of the plates 22 and 18 and the insulating layers 30 and 36.
  • the layer of insulation 28 forming the gate oxide of the transistor 12 is 100 angstroms and the layer of insulation 30 forming the dielectric of the storage capacitor 16 is also 100 angstroms, with the layer of insulation 36 being .1 microns and each of the plates 18 and 24 being .2 microns.
  • the N+ diffusion regions 20 and 32 each extend .3 microns from their respective sidewalls of the trench 24. With a spacing between adjacent cells of an array of cells along the word line direction equal to 1.2 microns and along the bit/sense line direction, which is orthogonal to that of the word line direction, equal to 1.0 microns the semiconductor substrate cell size is equal to only 5.75 square microns.
  • the capacitance of the storage capacitor 16 versus the capacitance of the bit/sense line 22, assuming 64 cells per bit/sense line provides a very desireable transfer ratio of at least 13%.
  • Fig. 4 is a plan view of an array of cells of the type illustrated in Figs. 2 and 3 of the drawings, wherein like reference characters refer to similar elements, with two cells 10A and 10B aligned in the horizontal direction along a word line 38A and two cells 10C and 10D aligned in the horizontal direction along a word line 38B.
  • the cells 10A and 10C are also aligned in the vertical direction along bit/sense line 22A and the cells 10B and 10D are aligned in the vertical direction along bit/sense line 22B.
  • Fig. 5 is a sectional view of Fig.4 taken through line 5-5 thereof
  • Fig. 6 is a sectional view of Fig. 4 taken through line 6-6 thereof
  • Fig. 7 is a sectional view of Fig. 4 taken through line 7-7 thereof to more clearly show the details of the elements of the cells 10A, 10B, 10C and 10D of the array.
  • Figs. 4 and 5 wherein Fig. 5 is taken through the isolation trench 42, it can be readily seen that the cells 10A and 10C are located within a trench 24A with a polyimide insulating segment 44 separating these cells 10A and 10C, and the cells 10B and 10D are located within a trench 24B with another polyimide insulating segment 44 separating these two cells 10B and 10D.
  • the bit/sense lines 22A and 22B extend vertically throughout the array in contact with the N+ diffusion regions 32 of the cells 10A and 10C and cells 10B and 10D, respectively.
  • each of the bit/sense lines 22A and 22B has an independent plate line to which different and independent voltages may be applied depending upon design considerations.
  • each of the capacitor plates 18 extends along its respective trench 24A or 24B.
  • Figs. 4 and 6 of the drawings wherein Fig. 6 is taken through the device trench 24A, it can be seen that the gates 14 of the cells 10A and 10C are separated from each other by the polyimide segments 44 and from the P- silicon substrate region 26 by the thin layer of silicon dioxide 28. Furthermore, by referring to Fig. 7 of the drawings, the isolation trenches 42 can be seen more clearly passing through the silicon substrate 26. Also, Fig. 7 shows the word lines 38A and 38B isolated from the silicon substrate 26 by the insulating layer 28.
  • each isolation trench 42 may be equal to approximately 1.0 microns, with the depth being equal to that of the depth of the device trenches 24A and 24B, and the separation between device trenches 24A and 24B may be equal to approximately 1.2 microns.
  • precharge and sense amplifier circuits 48 may be used to select any one or more of the cells 10A, 10B, 10C and 10D.
  • the isolation trenches 42 shown in Figs 3, 4, 6 and 7 may be formed by known reactive ion etching techniques in the silicon substrate 26 first and filled with an insulating material such as silicon dioxide.
  • the device trenches 24A and 24B are then formed in the substrate 26 orthogonally with respect to the direction of the isolation trenches 42.
  • a layer of doped insulation 34 as indicated in Fig.8 of the drawings is then chemically vapor deposited on the sidewalls and bottom of the device trenches 24A and 24B and on the upper surface of the substrate 26.
  • the doped insulating layer 34 is removed from the bottom of the trenches 24A and 24B and from the upper surface of the substrate 26, leaving only segments of the doped insulating layer 34 on the sidewalls of the trenches 24A and 24B, as indicated in Fig. 8 of the drawings.
  • the dopant which may be arsenic or phosphorous
  • the dopant in the layer 34 is driven into the sidewalls of the trenches 24A and 24B to form the N+ diffusion regions 20 and 32, as also indicated in Fig. 8 of the drawings.
  • any appropriate wet etchant such as potassium hydroxide (KOH), may be used to remove the segments of the doped insulating layer 34.
  • the layer of silicon dioxide 30 is grown on the sidewalls and bottom of the trenches 24A and 24B, as well as on the upper surface of the substrate 26 to provide the dielectric layer for the storage capacitor 16.
  • a layer of photoresist 50 is deposited over the silicon dioxide layer 30 and appropriately masked and etched so as to protect only that portion of the silicon dioxide layer 30 on the sidewall of the trenches 24A and 24B adjacent to the N+ diffusion region 20 required for the dielectric layer of the storage capacitor 16.
  • the unwanted portions of the silicon dioxide layer 30 are then removed by the use of any suitable etchant, such as a carbon tetrafluoride (CF4) plus oxygen (O2) plasma or a wet etchant, potassium hydroxide. Any appropriate wet etchant may be used to remove the remaining portions of the photoresist layer 50.
  • a suitable etchant such as a carbon tetrafluoride (CF4) plus oxygen (O2) plasma or a wet etchant, potassium hydroxide.
  • CF4 carbon tetrafluoride
  • O2 oxygen
  • a wet etchant potassium hydroxide
  • a conductive layer preferably copper-doped aluminum or tungsten or titanium silicide, is deposited within the trenches 24A and 24B and on the surface of the substrate 26 and appropriately removed by reactive ion etching techniques from the bottom of the trenches 24A and 24B and from the upper surface of the substrate 26 to form the storage capacitor plate 18 and the bit/sense line 22, as shown in Fig. 10 of the drawings.
  • the layer of insulation 36 is deposited over the entire structure and by reactive ion etching techniques, the layer of insulation 36 is removed from the bottom of the trenches 24A and 24B and from the surface of the semiconductor substrate 26, as indicated in Fig. 10 of the drawings.
  • the thin layer of silicon dioxide 28 is grown at the bottom of the trenches 24A and 24B and at the upper surface of the substrate 26 followed by the deposition of polysilicon or titanium silicide to form the gate 14 and the word lines 38A and 38B, as indicated more clearly in Fig. 2 of the drawings.
  • the layer of insulation 36 formed on the capacitor plate 18 and on the bit/sense line 22 may be made of silicon oxynitride (SiNO) or silicon nitride (Si3N4). If tungsten is used as the metal for the capacitor plate 18 and the bit/sense line 22, it is preferred that a thin layer of polysilicon be deposited over the tungsten in order to provide a thin layer of tungsten silicide over the tungsten. Additionally, a layer of silicon oxynitride (SiNO) may be deposited over the layer of grown silicon dioxide 28 to form the gate oxide of the transistors 12 of the storage cells 10A, 10B, 10C and 10D.
  • SiNO silicon oxynitride
  • an improved dynamic memory cell has been provided in a vertical structure within a semiconductor substrate requiring a very small substrate surface area by forming within a vertical trench or groove the storage capacitor, the transfer device and the highly conductive bit/sense line of the cell.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Computer Hardware Design (AREA)
  • Semiconductor Memories (AREA)
  • Semiconductor Integrated Circuits (AREA)

Claims (11)

  1. Cellule de mémoire vive dynamique à structure verticale à haute densité comprenant un substrat semi-conducteur (26) d'un premier type de conductivité, dans lequel est formée une tranchée (24) qui contient un condensateur de stockage (16),une ligne de bit/détection (22) et un dispositif de transfert (12), ledit dispositif de transfert étant disposé entre ledit condensateur de stockage et ladite ligne de bit/détection, et ladite ligne de bit/détection étant disposée le long d'une paroi latérale de ladite tranchée (24),
    caractérisée en ce que
       ledit condensateur de stockage (16) comprend une première région de diffusion (20) d'un deuxième type de conductivité, disposée le long d'une première paroi latérale, et une plaque conductrice (18) disposée dans la dite tranchée (24),
       ladite ligne de bit/détection (22) est métallique et disposée dans ladite tranchée (24) le long d'une deuxième paroi latérale opposée à ladite première paroi latérale de la tranchée, ladite ligne de bit/détection (22) comprenant une deuxième région de diffusion (32) du dit deuxième type de conductivité, disposée le long de ladite deuxième paroi latérale, et une couche conductrice disposée dans ladite tranchée en contact direct avec ladite deuxième région de diffusion, et
       ledit dispositif de transfert (12) est placé dans ladite tranchée (24), entre ledit condensateur de stockage (16) et ladite ligne de bit/détection (22), et il a une électrode de grille (14) séparée du fond de ladite tranchée par une couche d'isolation (28).
  2. Cellule de mémoire vive suivant la revendication 1, caractérisée en ce que
       la plaque conductrice (18) du condensateur de stockage (16) est séparée de ladite première région de diffusion (20) par un milieu isolant (30).
  3. Matrice de mémoire, caractérisée en ce qu'elle est constituée par un agencement de cellules de mémoire vive suivant la revendication 1, ledit agencement comprenant
       ledit substrat semi-conducteur (26) qui comporte une pluralité de tranchées parallèles (24A,B) et une pluralité de régions d'isolation allongées disposées dans une direction perpendiculaire à la direction desdites tranchées de façon à définir une pluralité de régions de cellule, chacune desdites cellules de mémoire vive étant située dans une région respective desdites régions, chacune desdites cellules de mémoire vive incluant un transistor (12) comme dit dispositif de transfert, et comprenant
       une pluralité de dites lignes de bit/détection (22), chaque ligne étant disposée dans une tranchée respective desdites tranchées (24) le long de la deuxième paroi latérale et en contact électrique avec une pluralité de dites deuxièmes régions de diffusion (32) disposées sur ladite deuxième paroi latérale dans ladite tranchée respective.
  4. Matrice de mémoire suivant la revendication 3, caractérisée en ce que
       les transistors sont des transistors à effet de champ (12).
  5. Matrice de mémoire suivant la revendication 3 ou 4, caractérisée en ce que
       une pluralité de lignes de mot parallèles (38) sont disposées dans une direction perpendiculaire à la direction desdites tranchées (24) et en contact avec les dites électrodes de grille (14), et
       chacune desdites lignes de bit/détection (22) est disposée dans une tranchée respective (24) sur la paroi latérale de celle-ci en face de ladite première paroi latérale.
  6. Matrice de mémoire suivant la revendication 5, caractérisée en ce que
       chacune desdites lignes de mot (38) et les électrodes de grille (14) en contact avec la ligne de mot respective constituent une structure intégrale en polysilicium dopé.
  7. Matrice de mémoire suivant la revendication 3 ou 5, caractérisée en ce que
       ladite pluralité de lignes de bit/détection (22) sont des films métalliques.
  8. Matrice de mémoire suivant la revendication 3 ou 5, caractérisée en ce que
       lesdites lignes de bit/détection (22) sont en siliciure de titane.
  9. Matrice de mémoire suivant la revendication 3 ou 5, caractérisée en ce que
       lesdites lignes de bit/détection sont en aluminium dopé au cuivre.
  10. Matrice de mémoire suivant la revendication 3 ou 5, caractérisée en ce que
       lesdites lignes de bit/détection sont en tungstène.
  11. Matrice de mémoire suivant la revendication 5 ou 7, caractérisée en ce que
       lesdites électrodes de grille (14) et les dites lignes de mot (38) sont en siliciure de titane et ledit substrat semi-conducteur (26) est en silicium, et la matière isolante comprend des segments de dioxyde de silicium et des segments de polyimide.
EP87104940A 1986-05-02 1987-04-03 Mémoire dynamique structurée verticalement à haute densité Expired EP0248993B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US06/858,787 US4811067A (en) 1986-05-02 1986-05-02 High density vertically structured memory
US858787 1986-05-02

Publications (2)

Publication Number Publication Date
EP0248993A1 EP0248993A1 (fr) 1987-12-16
EP0248993B1 true EP0248993B1 (fr) 1991-08-14

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EP87104940A Expired EP0248993B1 (fr) 1986-05-02 1987-04-03 Mémoire dynamique structurée verticalement à haute densité

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US (1) US4811067A (fr)
EP (1) EP0248993B1 (fr)
JP (1) JPH06105769B2 (fr)
AU (1) AU586096B2 (fr)
BR (1) BR8701781A (fr)
CA (1) CA1277031C (fr)
DE (1) DE3772109D1 (fr)
ES (1) ES2025082B3 (fr)

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Also Published As

Publication number Publication date
EP0248993A1 (fr) 1987-12-16
US4811067A (en) 1989-03-07
ES2025082B3 (es) 1992-03-16
JPH06105769B2 (ja) 1994-12-21
DE3772109D1 (de) 1991-09-19
AU7244487A (en) 1987-11-05
BR8701781A (pt) 1988-02-09
AU586096B2 (en) 1989-06-29
CA1277031C (fr) 1990-11-27
JPS62262456A (ja) 1987-11-14

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